In an optical transport network (OTN) hierarchy of an OTN transmission scheme, various multiplexing schemes are defined. It is desirable that a transmission device can support various multiplexing schemes. When each interface of a transmission device has a function of selecting a different multiplexing scheme, each interface needs to include a clock circuit for frequency-reproducing a communication rate of each different optical data unit (ODU) frame, a multiplexing/demultiplexing circuit of each multiplexing scheme, and a stuff circuit. Particularly, in an OTN communication scheme, since a communication frequency slightly differs according to an ODU frame (asynchronous communication), an oscillator phase locked loop (PLL) circuit needs to be separately provided. For this reason, a transmission device with a function of selecting different multiplexing schemes has a problem in that a circuit is complicated, and the cost and the power consumption of the transmission device increase.
For this reason, in a general transmission device, the circuit size is reduced such that only a circuit for a predetermined multiplexing scheme is installed in each interface.
Further, a transmission device includes a backup interface in order to cope with a problem of an active interface, and preferably performs communication path switching control of switching to the backup interface when the active interface has a problem.
A general transmission device executes communication path switching control by performing the following process.
A transmission device includes a backup interface corresponding to each active interface, and performs control such that a transmission device of a switching source matches a transmission device of a switching destination in a communication control state. Further, the transmission device of the switching source duplicates one client signal to a plurality of same signals, outputs the plurality of same signals to the active interface and the backup interface, and the transmission device of the switching destination selects any interface of the current system and the backup system which is to use a received signal.
Patent Document 1 discloses a technique of performing path switching by mapping two or more types of client signals to a frame of a format and performing time division multiplexing (TDM) on the corresponding signal.
Further, Patent Document 2 discloses a technique of adjusting a bit rate of two or more types of client signals to a rate range that can be included in a digital frame.